PROJECT SUMMARY/ABSTRACT The overall goal of this proposal is to bridge two major unsolved problems in basic and translational vision research: the functional role of rhodopsin dimerization and the pathophysiological mechanisms of retinitis pigmentosa, an inherited degenerative disease of the retina. Many mutations that cause retinitis pigmentosa are in the gene encoding the G protein-coupled receptor (GPCR) rhodopsin. Recent work has shown that three rhodopsin mutations, including F45L and F220C considered in this application, fail to dimerize in vitro. The central hypothesis of this proposal is that the inability of the F45L and F220C mutants to dimerize impedes normal photoreceptor function, ultimately leading to photoreceptor degeneration. This hypothesis will be tested using knock-in mouse models bearing either the F45L or the F220C rhodopsin mutation. Three Specific Aims are proposed. First, we will quantitatively describe the extent and time course of photoreceptor degeneration in each mouse, analyze photoreceptor ultrastructure, and examine rhodopsin trafficking. Second, we will analyze the status of rhodopsin dimerization in the native photoreceptor membranes of these mice. Third, we will investigate the ability of these mutants to support phototransduction through a combination of biochemical and electrophysiological approaches. Taken together, the proposed studies are likely to contribute to our basic understanding of the role that receptor dimerization plays in GPCR signaling and the pathophysiological mechanisms underlying visual loss in congenital blinding diseases.